Axonal spheroids preferentially form at presynaptic terminal regions in many of the collaterals of central branches of the axons, i.e. in the posterior funiculus nuclei, posterior column and posterior funiculus. Axonal dystrophy in normal ageing is essentially a morbid process restricted to the terminal parts of the axon.
Full Answer
Where is the posterior funiculus located?
The posterior funiculus is located between the posterior median septum and the medial edge of the horn ( Fig. 9.3 ). At cervical levels, this area consists of the gracile and cuneate fasciculi; collectively, these are commonly referred to as the posterior ( dorsal) columns.
What is the difference between funiculus and fasciculus?
A large group of axons which are located in a given area is called a funiculus (e.g. posterior funiculus ). Smaller bundles of axons, which share common features within a funiculus are called fasciculus (e.g. fasciculus gracilis).
What is a funiculus of a nerve?
A funiculus is a small bundle of axons (nerve fibres), enclosed by the perineurium. A small nerve may consist of a single funiculus, but a larger nerve will have several funiculi collected together into larger bundles known as fascicles. Fascicles are bound together in a common membrane, the epineurium. [1] [2]
What are Funiculi in the spinal cord?
Funiculus (neuroanatomy) A small nerve may consist of a single funiculus, but a larger nerve will have several funiculi collected together into larger bundles known as fasciculi. Fasciculi are bound together in a common membrane, the epineurium. Funiculi in the spinal cord are portions of white matter. Examples include:
What is found in the posterior funiculus?
The posterior funiculus contains large myelinated nerve fibers of posterior root ganglion cells. The peripheral processes of these ganglion cells form or innervate sensory receptors in the skin and deep tissues of the body.
Which nerve tracts run in the posterior funiculus?
The posterior funiculus contains the ascending spinobulbar tract which is made up of the cuneate and gracile fasciculi.
Is the posterior funiculus white or gray matter?
white matterone of the three major subdivisions of white matter in the spinal cord, the posterior funiculi contain ascending pathways carrying sensory information to the brain.
What does the funiculi of the spinal cord contain?
A funiculus or columnis a small bundle of axons (nerve fibres), enclosed by the perineurium. A small nerve may consist of a single funiculus, but a larger nerve will have several funiculi collected together into larger bundles known as fascicles. Fascicles are bound together in a common membrane, the epineurium.
What are the three types of funiculi?
Latin for "string," funiculus refers to a bundle of nerve fibers and is specifically used to refer to one of the three subdivisions of white matter in the spinal cord: the anterior, posterior, and lateral funiculi.
Which part of the spinal cord contains axons carrying signals for proprioception?
The spinocerebellar tracts carry unconscious proprioceptive information gleaned from muscle spindles, Golgi tendon organs, and joint capsules to the cerebellum. The cell bodies of the primary sensory neurons that bring this information from such receptors to the spinal cord are located in the dorsal root ganglia.
What is grey matter in the spinal cord?
The grey matter also extends from the brain into the spinal cord. The grey matter creates a hornlike structure throughout the inside of the spinal cord while the white matter makes up the surrounding sections of the spinal cord. The grey matter does extend to the spinal cord to make signaling more effective.
Where is the white matter in the spinal cord?
White matter in the spinal cord is sometimes called superficial tissue because it is located in the outer regions of the brain and spinal cord. Gray matter is situated closer to the center of the central nervous system.
Where is the grey matter in the brain?
Gray matter, named for its pinkish-gray color, is home to neural cell bodies, axon terminals, and dendrites, as well as all nerve synapses. This brain tissue is abundant in the cerebellum, cerebrum, and brain stem. It also forms a butterfly-shaped portion of the central spinal cord.
What is the difference between the white columns and the tracts of the spinal cord white matter?
Just as the gray matter is separated into horns, the white matter of the spinal cord is separated into columns. Ascending tracts of nervous system fibers in these columns carry sensory information up to the brain, whereas descending tracts carry motor commands from the brain.
How many funiculus does the spinal cord have?
In each half of the spinal cord, white matter is divided into three major bundles, called funiculi. The dorsolateral sulcus marks the division between dorsal funiculus and lateral funiculus.
What is true of all of the axons within a particular tract?
What is true of all of the axons within a particular tract? They carry information to approximately the same location.
Where are ascending and descending tracts located?
The spinal cordThe spinal cord has numerous groups of nerve fibers going towards and coming from the brain. These have been collectively called the ascending and descending tracts of the spinal cord, respectively. The tracts are responsible for carrying sensory and motor stimuli to and from the periphery (respectively).
What tracts are in the lateral funiculus?
The lateral funiculus (Figs. 9.3 and 9.12; Table 9.1) contains the lateral corticospinal and rubrospinal tracts as well as other more diffusely organized fiber populations (reticulospinal, fastigiospinal, raphespinal, hypothalamospinal).
Where does the corticospinal tract synapse?
Description. The neurons that travel in the corticospinal tract are referred to as upper motor neurons; they synapse on neurons in the spinal cord called lower motor neurons, which make contact with skeletal muscle to cause muscle contraction.
Is the spinal cord posterior column of white matter composed of sensory tracts?
The white matter of the spinal cord is subdivided into dorsal (or posterior), lateral, and ventral (or anterior) columns, each of which contains axon tracts related to specific functions. The dorsal columns carry ascending sensory information from somatic mechanoreceptors (Figure 1.11B).
Where is the dorsal horn located?
At the region where the dorsal horn reaches the pial surface of the spinal cord, there is a prominent band of fibers called the dorsolateral fasciculus (the tract of Lissauer). This tract contains primary afferent fibers, which either ascend or descend for a few segments before entering the dorsal horn. The dorsal column of white matter is chiefly made up of the central processes of dorsal root ganglion cells. These large myelinated axons form the main pathway conveying skin sensation and position sense (proprioception) from the limbs and trunk to the brain. Because more fibers are added at each segment in a caudorostral order, the dorsal column is very small in sacral segments, and largest in the rostral cervical spinal cord. As the fibers from one segment enter the dorsal column, they move to form a strip as close to the medial edge as possible. Fibers from the next segment move as far medially as they can and form a strip lateral to those of the more caudal segment. When viewed at high cervical levels, the fibers from lower thoracic, lumbar and sacral segments (segments below T6) form a distinct medial strip, the gracile fasciculus. The more lateral group is wedge-shaped and is called the cuneate fasciculus. It primarily contains afferents from the upper thoracic and cervical segments.
Which fasciculus is involved in visual processing?
Interestingly, it was demonstrated that stimulation of the anterior part of the inferior longitudinal fasciculus, in front of the visual word form area (i.e., the basal part of the temporo-occipital junction, involved in high-level visual processing such as reading), as well as stimulation of the uncinate fasciculus, never generated transient language disturbances, and thus could be removed with no aphasia. It seems that this indirect pathway from the temporo-occipital areas to the prefrontal region, with a relay at the level of the temporal pole (temporo-occipital area, inferior longitudinal fasciculus, temporal pole, uncinate fasciculus, orbito-frontal and prefrontal areas) can be compensated by the direct pathways constituted by the IFOF. 12
How does syringomyelia occur?
An early theory was that syringomyelia arose from the prevention of normal flow of CSF by congenital failure of opening of the outlets of the fourth ventricle (foramina of Luschka and Magendie). 90 A pulse wave of CSF pressure, generated by systolic pulsation of the choroid plexuses, is transmitted into the spinal cord via the central canal, resulting in dilatation of the central canal, with a diverticulum that ramifies from the central canal and dissects along gray matter and white matter tracts. Indeed, the frequent association of syrinx with craniocervical junction malformations, which could potentially block the flow of CSF, supports this theory. In a more recent report, it was postulated that the primary event in the formation of syrinx in many cases is reduced volume of the posterior cranial fossa, such as that caused by basilar invagination, with resultant Chiari malformation caused by caudal displacement of structures. Long-standing pulsatile pressure of the herniated structures on the spinal cord leads to syrinx formation as a tertiary event. It was suggested that this was a mechanism serving to protect vital neural structures at the level of the craniovertebral junction at the cost of spinal cord. One report questioned prevailing hydrodynamic theories, on the basis of the facts that syrinx pressure exceeds CSF pressure and the composition of syrinx fluid is not identical to that of CSF. 89 An alternative theory is abnormal spinal cord structure, with a tendency to cavitate. 57,87
When does syringomyelia start?
Types I and II syringomyelia are sporadic and usually begin in middle age; in some cases, an abnormality may be evident at birth. Symptoms develop insidiously, although there are reports of sudden and dramatic worsening after violent strain or a paroxysm of coughing. 57 Intermittent progression is the usual course, with patients being bedridden within 5 to 10 years; however, the course is extremely variable, and some patients remain stable for many years. 57
Where is the pyramidal tract located in dolphins?
Pyramidal tract. In the dolphin, this important tract originates in the neocortical motor area rostral to the “cruciate” sulcus ( Figs. 6.14 and 6.15) and runs through the internal capsule in the caudal direction ( Fig. 6.29; see also Chapter 10, Fig. 10.4 ). At mesencephalic levels, the pyramidal tract is seen in the corticobulbar and corticopontine tracts ( Fig. 6.26, cob, cop) but is already very small at anterior medullary levels ( Fig. 6.43 b). Typical compact fiber bundles (pyramids), as seen in terrestrial mammals behind the pons, are not present in cetaceans. Here, the pyramidal tract is weak and situated lateral to the inferior olivary complex so that both inferior olives join midsagittally ( Figs. 6.27, 6.32a, and 6.51d ). Obviously, most of the pyramidal motor fibers are relayed in the pontine nuclei, which have strong projections to the cerebellum (see Section “Pons and Cerebellar Connections” in this chapter). Perhaps the extremely well-developed inferior olives, more specifically, the rostral medial accessory olive, which occupies the ventromedial area in the medulla, have pushed the residual pyramidal tracts aside during development. In dolphins, the crossing of the pyramidal tracts (decussation) is indistinct and the proceeding of the tracts hardly visible. Also, it is unlikely that in these animals, corticospinal fibers descend more than a few cervical segments in the spinal cord ( Fig. 6.52 ). This pattern resembles much that seen in hoofed animals and the elephant. r In many terrestrial mammals (ungulates), the corticospinal tract is small and the rubrospinal tract is strongly developed. In cetaceans, both the corticospinal and rubrospinal tracts are small ( Verhaart, 1970 ), which seems to be a specialty of these aquatic animals. As kind of a compensation, their mass movements of the body stem may rather be generated and maintained by the projections of Deiters’ nucleus (lateral vestibulospinal tract), the olivospinal tract as well as the reticulospinal tract.
Which part of the trigeminal nucleus is the ipsilateral trigeminothalamic?
Trigeminothalamic tract. The dorsal part of the principal sensory trigeminal nucleus gives rise to the ipsilateral dorsal trigeminothalamic tract ( Voogd et al., 1998 ). The latter joins the trigeminal lemniscus and terminates in the medial part of the ventral posterior thalamic nucleus as the main somatosensory thalamic nucleus (see Section “ Thalamus ” in this chapter). The projection from the main sensory trigeminal nucleus to the medial part of the ventral posterior thalamic nucleus (Wallenberg’s tract) is remarkably large in cetaceans. In dolphins, it may be involved in the operation of the blowhole (epicranial) complex with respect to sound and ultrasound generation and emission ( Oelschläger and Oelschläger, 2002 ).